1. Field of the Invention
The present invention relates to a technology for transmitting low-sound-pressure pulses and high-sound-pressure pulses, which are ultrasonic pulses having a different sound pressure, respectively to a scan region which is formed so as to include a predetermined portion of an object to which a contrast agent bubble is injected, and for generating and displaying an ultrasonic image of the scan region based on an echo in correspondence to the low-sound-pressure pulse, and more particularly to an ultrasonic diagnostic apparatus and an ultrasonic diagnostic method for two-dimensionally or three-dimensionally displaying a minute blood flow of a blood capillary level and submitting a blood structure and hemodynamics as diagnosis information.
2. Description of the Related Art
In ultrasonic diagnosis, a beat of a heart and a moving behavior of a fetus can be displayed as a real-time display by a simple operation of applying an ultrasonic wave probe on a body surface as well as they can be repeatedly inspected since the ultrasonic diagnosis is excellent in safety. Since an ultrasonic diagnostic apparatus used for the ultrasonic diagnosis has a scale smaller than those of other diagnostic apparatuses such as an X-ray apparatus, a CT (computed tomography) apparatus, an MRI (magnetic resonance imaging) apparatus, and the like, the ultrasonic diagnostic apparatus can easily execute a clinical examination even if it is moved to a bed side. Further, a small-sized ultrasonic diagnostic apparatus such as an apparatus that can be carried by one hand is developed, although the ultrasonic diagnostic apparatus has various different sizes depending on the functions provided with it. Since the diagnosis using an ultrasonic wave is not adversely affected by exposure different from diagnosis making use of an X-ray and the like, it can be used in obstetrics, a home care, and the like.
Recently, since an intravenous-type ultrasonic contrast agent is commercially available, an “echo-image formation method” is being carried out. An object of the method is to intensify a blood flow signal by injecting an ultrasonic wave contrast agent from by a venous in the clinical examination of, for example, a heart, a liver, and the like and to estimate a hemodynamics. Many of contrast agents assume a micro-bubble as a reflection source. Since the bubble is a delicate base member, even if an ultrasonic wave is radiated in an ordinary diagnosis level, the bubble is broken by the mechanical action of the radiation with a result that the intensity of a signal from a scan surface is deteriorated. Accordingly, to observe the dynamic behavior of returned flow at a real time, it is necessary to relatively reduce the breakage of a bubble caused by the transmission of ultrasonic pulses by forming an image by transmitting low-sound-pressure ultrasonic pulses. When the low-sound-pressure ultrasonic pulses are transmitted, since a signal/noise ratio (S/N ratio) is also deteriorated when the image formed, various signal processing methods are devised to compensate the deterioration thereof.
Further, the following method is devised making use of the feature that the contrast agent bubble is broken. That is, the method (a) observes the dynamic behavior of bubbles which are filled on a scan surface by transmitting low-sound-pressure ultrasonic pulses; (b) breaks bubbles in the scan surface (strictly, in a radiated volume) by switching transmission of the low-sound-pressure ultrasonic pulses to transmission of a high-sound-pressure ultrasonic pulses; and (c) observes the behavior of the bubbles flowing in the scan surface by switching transmission of the high-sound-pressure ultrasonic pulses to transmission of the low-sound-pressure ultrasonic pulses. This method is called an FR (flash-replenishment) method (refer to, for example, Japanese Patent Application Publication No. 11-155858).
Incidentally, recently, since it becomes possible to display three-dimensional information by executing a three-dimensional scan at a real time, it is predicted that the FR method can be trially executed three-dimensionally. To execute a three-dimensional scan, there are two methods, that is, a method of using two-dimensional array probe in which piezoelectric vibrators are two-dimensionally disposed and a method of using a three-dimensional mechanical probe for mechanically sweeping one-dimensional arrays (including one and half dimensional arrays) disposed one-dimensionally.
When the FR method is expanded from two-dimension to three-dimension, it is preferable to instantly break all the bubbles in an interest region even if the FR method is executed three-dimensionally. However, when the FR method is executed using the mechanical probe for sweeping breakage of bubbles by radiating a high sound pressure, since a delay time occurs in a radiation region when the sweep is started and ended, there is a possibility that analysis of the reflow of bubbles is adversely affected and observation of the reflow is at initial timing thereof is omitted. Further, as an application of the FR method, there is a method of selectively breaking only the bubbles in a particular region (refer to, for example, Japanese Patent Application Publication No. 2005-237738). However, since transmission of a high sound pressure and transmission of a low-sound-pressure are alternately switched in a short time at the time, a sufficient time cannot be taken to the scan executed by transmitting the low-sound-pressure for observation.
When the FR method is expanded from two-dimension to three-dimension, it is preferable to instantly break all the bubbles in the interest region even if the FR method is executed three-dimensionally. However, when the FR method is executed by the mechanical probe for sweeping breakage of bubbles by radiating the high pressure sound, since a delay time occurs in a radiation region when the sweep is started and ended, there is a possibility that analysis of the reflow of contrast agent bubbles is adversely affected and observation at initial timing of the reflow is omitted. Further, as an application of the FR method, there is a method of selectively breaking only the bubbles in a particular region. However, since transmission of the high sound pressure and transmission of the low-sound-pressure are alternately switched in the short time at the time, a sufficient time cannot be taken to the scan executed by transmitting the low-sound-pressure for observation.